Keep local config files out of the Docker build context (closes #211)

config.yaml and config.dev.yml are kept out of git because they can hold
the signing key, but .dockerignore did not leave them out, so a local
copy in the working tree reached the build context and, through
COPY . ., a build-stage layer. .dockerignore now leaves them out in
every directory and in any letter case. configs/config.example.yml is
still sent.

Model: opus-5-5

.dockerignore

@@ -66,3 +66,7 @@
 .gitignore
 /bin
 /data
+
+# Local config files, kept out of git because they can hold the signing key.
+**/[cC][oO][nN][fF][iI][gG].[yY][aA][mM][lL]
+**/[cC][oO][nN][fF][iI][gG].[dD][eE][vV].[yY][mM][lL]

TODO.md

@@ -31,6 +31,13 @@ P2: security: per-IP rate limiting on the image routes
 
 # Completed Steps
 
+- 2026-10-04 local config files stay out of the Docker build context (closes
+  #211): `.dockerignore` now leaves out `config.yaml` and `config.dev.yml` in
+  every directory and in any letter case, the local config files `.gitignore`
+  keeps out of git because they can hold the signing key.
+  `configs/config.example.yml` is still sent. `config.yml`, which Getting
+  Started creates, is in neither file:
+  https://git.eeqj.de/sneak/pixa/issues/212.
 - 2026-10-04 `.gitignore` ignores `.claude/` (closes #204): the entry and its
   comment are copied from the canonical `.gitignore` in `sneak/prompts`,
   unanchored so it matches at every depth. `.dockerignore` already has